Stirring-roll for a continuous cast machine of metallic products of large cross section

ABSTRACT

Stirring roll comprising:
         (a) a shell ring  1  made of nonmagnetic steel in rotation of axis A-A and intended to come into contact with the surface of a large face of the cast slab ( 6 ),   (b) mechanical-connection members, arranged on each side of the shell ring to support the shell ring while leaving it free to rotate axially,   (c) support elements  4  which are offset on either side beyond the limits of the shell ring and fixed to the rigid frame  5  of the casting machine,   (d) internal electromagnetic equipment consisting of at least one polyphase linear inductor  8  mounted coaxially with respect to the shell ring so as to leave between the two an annular space  11  through which a cooling liquid can circulate, and which constitutes an axial shaft provided with terminal extensions  20  that rest, without the ability to rotate axially, on the fixed support elements  4  and which are hollow so as to allow the passage of the cooling liquid and of the electrical connections of the inductor, and   (e) inlet/outlet casings  16  for the cooling liquid which are provided with electrical connection terminals  18   a,    18   b  and mounted at the ends of the terminal extensions  20  of the inductor beyond the fixed support elements  4;  
 
this stirring roller, which is characterized in the shell ring bears against said terminal extensions ( 20 ) of the inductor ( 8 ) via rolling bearings ( 3 ), has been designed to be suitable also for the casting of extra-wide slabs.

The present invention relates to electromagnetic equipment with asliding magnetic field for setting in motion the still molten liquidmetal within a large cross sectional metallic product, such as a steelslab, during its solidification, downstream of the ingot mold, in thesecondary cooling zone of the continuous casting unit that produces theslab.

More specifically, the invention concerns the manufacture of this typeof equipment, usually called “stirring roll” when it is connected with asupporting and guide roll for the cast slab, and made tubular for thispurpose.

It should be stated that the electromagnetic part of this type ofequipment traditionally comprises a polyphase linear inductor thatgenerates a movable magnetic field directed perpendicularly to thesurface of the shell of the roll that surrounds it and which slidesalong the rotational axis of said roll.

A quick review of this technology that is widely used today in the steelindustry throughout the world for the continuous casting of slabs,allows us to identify schematically three periods.

The first, that of the principle, is represented by the document FR72/20546 published in December 1973 which describes a polyphasic centrallinear inductor that is coaxially mounted with a non-magnetic steeltubular body that surrounds it. This was the birth of the stirring rollas an active piece of equipment capable of replacing one or a pluralityof pre-existing full-matter supporting and guide rolls on the castingmachine. The two fundamental versions were already disclosed therein: aninductor that turns with the shell of the roll (the tubular body) incontact with the surface of one of the large sides of the cast slab, ora fixed inductor.

The second period is that of the document FR 75/05623 published inAugust 1976 which states the basic technological concept of the stirringroller with a turning inductor; the concept is based on a tubular bodyand mechanical linking elements that ensure the support of the tubularbody while allowing it a free axial rotation. These elements areschematically constituted by a unit, formed, on each side of the tubularbody, by a tubular spindle in the shape of a truncated cone, mounted atthe end of the tubular body, and by a rolling bearing mounted on asupporting element located beyond the limits of the tubular body andfixed to the rigid frame of the caster, the small base of the spindlecoming to turn in said bearing. The central inductor is maintained andcentered in an internal space of the large base of each spindle. Atleast one of the spindles (detachable to allow the inductor to bemounted in the tubular body) extends past its support bearing to allowthe inductor to be electrically connected up to a polyphasic externalsupply.

The third period is that of the document EP-A-0 043 315 published inJanuary 1982. This document discloses in detail the successfuloperational achievement of the stirring roll, this time with a fixedinductor, which is still used today: again there is the same generalstructure as that of the turning inductor, except that the centralinductor in this case is held by its own internal core, on which arewound the electric phase windings. For this purpose this core forms anaxial shaft, whose ends of narrowed diameter pass by the small bases ofthe spindles of the tubular body to engage with the roller bearingssupporting the tubular body and fixed to the rigid frame of the castermachine by means of a flange lock mounted on the external side of thesebearings and which blocks the inductor against axial rotation.

Moreover, this flange constitutes the floor of a sealed water boxequipped with water inlets/outlets for cooling the tubular body and theinductor by circulation in the calibrated annular space that separatesthe inductor from the tubular body. The water box also acts as anelectrical connection panel and on the outside possesses electricterminals that connect the inductor to the external electricity supply.

As can be seen from the right hand side of FIG. 1, such a technology fora stirring roller of the prior art is essentially characterized overallby the cooperation of two distinct coaxial sub-assemblies, one free torotate axially, the other fixed, and both being carried by the supports4 of the tubular body 7 which are fixed to the rigid frame 5 of thecasting machine:

-   a first assembly, fixed in axial rotation, formed by the central    inductor 8, whose terminal extensions 12 rest on the centering    cradles 14 that block it against axial rotation and which are    integral with the rigid frame 5 of the caster by means of the    supporting elements 4;-   and a second assembly, mobile in axial rotation, formed by the    tubular body 1 intended to come into rolling contact with the cast    slab 6 and by its two tubular spindles 2 that lengthen it at each of    its ends so as to turn by their small base 13 in the projected    roller bearings 3 mounted on the supporting elements 4 fixed to the    rigid frame 5 of the caster.

For convenience, the water boxes 16, also acting as an electricalconnection panel 18 for the inductor, externally cover and seal thecradles 14.

This type of stirring roll, which has proved to be perfectly adapted toits dual function, support-stirring, is commonly used in the majority ofmachines for the continuous casting of slabs of standard width, i.e. upto about 1600-1700 mm, the width at which the tubular body supported bytwo end bearings is still sufficiently rigid so as not to sagunacceptably.

This type of stirring roll could also be used for very wide slabs,namely with a width of more than 2400 mm, by means of installing twohalf-rollers with an intermediate roller bearing in order to ensure therigidity and geometric straightness of such an assembly under the thermomechanical stresses imposed by the presence at its contact of a verywide slab that is solidifying (WO2011/117479).

On the other hand, this technology proves to be inapplicable for slabsof intermediate width, for example from 2000 mm to ±20% (therefore from1600 to 2400 mm to be precise). The presence of the end spindles makesthe active part of the inductor too short for considering the solutionwith two half-rollers with an intermediate bearing, and the solutionwith a single roller without an intermediate bearing would certainlylead to an inacceptable sag, especially as the presence of the endspindles separates the points of support on the rigid frame of thecasting machine far beyond the simple distance needed for covering thewhole width of the slab. For example, a stirring roll of 240 mm diametermounted at a distance of approximately 3 m below the level of the metalcast into an ingot mold in a “standard” casting machine with a width of1600 mm, sags less than 1 mm under the ferrostatic pressure of the slab,whereas in a machine with a width of 2000 mm the sag would be about 4mm, which is inacceptable.

In view of the above, and while retaining the functional and operationalqualities of the conventional stirring rolls in their entirety, theobject of the present invention is to propose a technological conceptfor them without end spindles in order to rigidify the tubular body, topermit a more economical production both in acquisition and runningcosts and in addition to be able to fulfil all requirements in terms ofwidth of the slabs from 1600 mm (or less) to 2400 mm (at most).

Accordingly, the subject matter of the invention is a stirring roll fora continuous casting machine of metallic products having a broad crosssection, such as a slab, comprising:

-   (a) at least one external axially rotating tubular body made of    non-magnetic steel intended to come into contact with the surface of    a wide face of the cast slab,-   (b) mechanical connection elements that ensure the support of the    tubular body while allowing it to freely rotate axially,-   (c) supporting elements of the stirring roll located on both sides    beyond the limits of the tubular body and fixed to the rigid frame    of the casting machine,-   (d) internal electromagnetic equipment consisting of at least one    polyphasic linear inductor with a sliding magnetic field, mounted    coaxially with the tubular body so as to provide an annular space    between them for the circulation of a cooling liquid, said equipment    forming an axial shaft equipped with hollow end extensions that    provide support that is blocked against axial rotation on said    support elements, and-   (e) inlet/outlet boxes for cooling liquid equipped with electrical    connection ports and mounted on the ends of the terminal extensions    of the inductor beyond said supporting elements;    stirring roll characterized in that the tubular body bears on said    terminal extensions of the inductor by means of said mechanical    connecting elements formed by the bearings located between the    tubular body and said terminal extensions (preferably at the ends of    the tubular body).

Clearly, the invention is based on the idea of making the inductor actas the support for the tubular body that turns around it in closeproximity. To this end the roller bearings of the tubular body, or moregenerally its mechanical connecting elements that leave it free foraxial rotation, are separated from their traditional supporting elementsintegral with the structure of the casting machine. By doing so, theterminal extensions of the inductor are exclusively received by thesupporting elements, while the roller bearings required to support thetubular body and allowing it free for axial rotation, therefore becomesimple bearings mounted on these terminal extensions of the inductor.

Among the principal advantages specific to the technology of thestirring rolls according to the invention, and which will be presentedin more detail below, we can already mention the elimination, or atleast a major reduction, of the phenomenon of “angular deflection” ofthe rollers in the bearings, because they have disappeared.

The technological concept according to the invention moreover opensparticularly attractive possibilities for a simplified embodiment ofextra-long stirring rolls, intended, as already emphasized, for machinesfor casting wide slabs (more than 1600 mm), whose trend is increasinglyconfirmed in the worldwide steel industry driven by ever increasingproductivity requirements of steel works.

In fact it is known that tubular rolls of great unit length can sagunacceptably from the ferrostatic pressure of the slab resting on them.To provide a solution to this problem, in another embodiment of theinvention which is accordingly advantageously applicable to the castingof wide slabs, such an extra-long stirring roll (hereinafter called“split stirring roll”) comprises not one but two separate alignedtubular bodies. These two tubular bodies preferably have the samelength, and are equipped with two additional intermediate bearings thatbear on a central intermediate extension of the axial core of theinductor. This intermediate extension is itself supported by asupplementary central support fixed to the rigid frame of the castingmachine.

It should be noted that an advantage that is specific to this variant isthe compactness of the central bearing zone of the split stirring roll,compactness impossible to achieve with end spindles and which naturallyleads to a more extensive, therefore better, mechanical support of thecast slab in the central zone of its large faces.

Another interest of the split stirring roll is operational in nature: inthe case of very wide slabs, for example greater than 2000 mm, twoinductors that are electrically and magnetically independent of oneanother can be mounted on the same axial frame for the inductors withinthe same stirring roll, while at the same time adapting a centralsupport fixed to the rigid frame of the caster.

In all the embodiments, the stirring roll according to the invention,compared with traditional stirring rolls of the prior art, ischaracterized by the fact that the end rolling bearings and the spindlesare eliminated and replaced by simple supports for a fixed, non-turningshaft represented by the terminal extensions of the inductor and thatthe tubular body turns around said fixed shaft by bearing on the latterby means of the bearings that hold it.

This arrangement leads to a marked decrease in the distance separatingthe fixed supports of the stirring roll, hence to a correspondingreduction of the sag of the tubular body in operation, and consequentlyreduces or obviates the phenomenon of angular deflection.

Moreover, the strain imparted by the tubular body on its connectingelements is no longer transmitted by the necessarily tubular and thusdeformable spindles, but is applied directly to a central shaft that canbe dimensioned as needed to avoid any deformation. Furthermore,transposed to the intermediate bearings in the version of the splitstirring roll, this arrangement ensures a minimum space between the twotubular bodies, and consequently a maximized continuity of support forthe slab across its width.

The invention will be well understood and other aspects and advantageswill appear when studying the following description that gives anexample of an embodiment of the stirring rolls according to theinvention with reference to the figures, in which:

FIG. 1 is a didactic representation, according to an axial section, of avoluntarily hybrid stirring roll for the purpose of comparison with theprior art, in the sense that the left extremity (in the figure) isrealized with the technology according to the invention, whereas theright extremity is shown in the usual form of the prior art;

FIG. 2 is an axial section of a stirring roll in its basic version witha single tubular body (thus without central support);

FIG. 3 is an axial section of a variant with two tubular bodies andcentral support, named “split stirring roll”.

Referring firstly as a reminder to the right hand side of FIG. 1, it canbe seen that a classic stirring roll is essentially formed by anextended tubular body that turns about its principal axis of symmetryA-A. This body consists of an envelope or tubular body 1, made ofnon-magnetic stainless steel and by frustoconical spindles 2 thatmaintain said tubular body at both of its ends, the small base 2 a ofeach spindle being engaged in a rolling bearing 3 incorporated into asupport 4 fixed to the rigid frame 5 of the continuous casting machine.

This casting machine can cast the metallic slabs 6 that progress from aningot in the top down to a lengthwise cutting tool at the bottom of themachine. At the same time starting from the periphery of the castproduct 6 the molten metal progressively solidifies under the effect ofan intense cooling of its surface by contact with the internal walls ofthe ingot mold, then by direct application of water in the secondarycooling stages of the casting machine, exactly there, where the stirringrolls that equip the machines are located.

In fact at this location the cast slab is maintained and guided in itsslow movement toward the turning bearing rollers that by a constantlyrenewed force generated by the rotation are pressed into contact on eachof the broad faces of the slab, such as the broad face 7 of the figure.

As can be seen, the available volume inside the tubular body 1 is almosttotally occupied by an electromagnetic inductor 8 intended to allow thestill molten metal to be set in motion in a controlled manner within theslab 6. For that purpose, the inductor 8 of the polyphasic linear typecomprises a magnetic shell 9 that serves as a winding support for thephase windings 10 that follow one another along the inductor so as to beable to generate a magnetic field that is directed on the wholeperpendicularly to the wide faces of the slab 6, but mobile, i.e.sliding along the axis A-A of the inductor when said windings 10 arecorrectly connected to the terminals of an external polyphasic (biphasicor triphasic) power source (not shown).

This inductor 8 is also an axially symmetrical body on its longitudinalaxis which merges with the axis A-A of the tubular body 1 in order to beable to be well centered on the latter while leaving an annular space 11between them for the circulation of a cooling fluid that will ensure thethermal maintenance of the stirring roll when in operation. This axialcentering is achieved with the help of cylindrical terminal extensions12 of the inductor of reduced diameter so as to be able to engage with aslight clearance in the small base 2 a of the spindle 2 and to exceedthe confines of the spindle past the bearing 3 by a projection 13 thatserves as a key to block the inductor against axial rotation at thelevel of an end plate 14 equipped with the necessary cotter pins. Eachterminal extension 12, which is hollow (axial channel 24) is providedwith radial ducts 15 communicating with the annular space 11, emerges ina water box 16 mounted in a water-tight manner at the extremity on theend plate 14 and provided with an inlet or outlet pipe 17 for thecooling water (shown as an outlet in the figure).

It can be seen that the water box 16 also serves as a panel withterminals 18 for connecting the inductor 8 to an external polyphasicelectricity supply, the connecting wires 19 of the inductor passing inthe axial hollow of its extension 12 to reach the terminals 18.

Referring now at will to FIG. 2 or to the left hand side of FIG. 1, itcan be seen that the stirring roll according to the invention (whosecomponent parts that are identical to those of the just-describedstirring roll of the prior art are designated with identical referencenumbers) differs from the classical technology of the prior art in thatthe rolling bearing 3 as well as the spindle on each end of the rollhave been eliminated. This singularity frees up space for the terminalextension 20 of the inductor 8 that then, blocked from rotation by awedge 31, comes to rest in the cradle formed by this fixed support 4.

As can be seen, but without it being mandatory, this extension 20 isplanned to be more massive with a greater diameter than that of theanalogous extension 12 of the classical stirring roll (right hand partof the figure); this is in order to reinforce as needed its mechanicalstrength, because greater demands will be placed on it at this point, aswill be understood from the following.

In fact, firstly the bearings 3 replace by themselves the end spindlesof the tubular body 1 (which are therefore eliminated) in theirretention and driving force functions when the body rotates, and,secondly, these bearings 3 come to bear directly on the terminalextension 20 of the inductor that accordingly serves to support thetubular body 1.

It should be noted that by eliminating the end spindles, the distancebetween the fixed supports 4 is consequently reduced by 25 to 40 cm,depending on the case, with respect to the technology of the prior art,i.e. nearly 20% of the length of the stirring roll.

A bearing 3 will therefore be fixed to each end of the tubular body.This fixing can be achieved, in a manner known per se, by means of abolted ring (not shown in the figures so as not to needlessly clutterthem). Similarly, it will be advantageous to provide an annular flange32 mounted on the end of the tubular body to act as a lubrication platefor the bearings 3 and which comes to cover said bearings to protectthem from dust and to improve the water-tightness of the assembly.

However, it will be advantageous, as already stated at the beginning, toopt, at least for one of the two ends, if not for both, for a cageassembly for the bearings which is “openable” in its mechanical designso as to facilitate the installation of the inductor 8 inside thetubular body 1 in the workshop.

FIG. 3 illustrates the technological variant of the invention applied inthe case where the stirring roll no longer has a single tubular bodythat extends over the whole width of the cast slab, but has twohalf-tubular bodies 1 a and 1 b.

These two collinear half tubular bodies are held close to their ends byintermediate bearings 3 c and 3 d and are separated from one another bya short distance (say between 10 and 20 cm) due to the presence betweenthem of an intermediate extension 20 c of the inductor. As the endbearings 3 a and 3 b bear on the terminal extensions 20 a and 20 b ofthe inductor, the intermediate bearings 3 c and 3 d bear on theintermediate extension 20 c of the inductor that for this reason is freeof electrical windings and bears on a central support 21 fixed to therigid frame 5 of the casting machine.

As already stated, a stirring roll of this type, called “split” for areason that is obvious from the above statement, and formed in fact bytwo half tubular bodies, designated 1 a and 1 b, is an adequate responseto the growing demand—at least in the steel industry—to be able tocontinuously cast slabs of greater width, easily exceeding the limits ofconventional stirring rolls of 1.6-1.7 m, even 2.4 m width and stillmore in a not too distant future, because this split roll is protectedagainst unacceptable sagging by the central support 21.

The terminal extensions of the inductor 20 a or 20 b, located at theends of the roll, are hollow so as to be able to emerge,

-   on one side, by their free end, into a water-tight water box 16 a or    16 b, provided with an inlet/outlet pipe 17 a or 17 b for the water    and whose panel with the terminals 18 a or 18 b forms one of the    walls (the front panel in the figure),-   and on the other side, into the annular space 11 a or 11 b, arranged    between each half tubular body 1 a or 1 b and the inductor 8 by    means of radially drilled ducts 15 a or 15 b.

The intermediate extension 20 c is also hollow and provided withradially drilled ducts 15 c, 15 d so as to form a water-tight centralduct communicating between the annular spaces 11 a and 11 b.

The cooling of the half tubular bodies 1 a and 1 b and the inductor 8 isthus ensured by a common water circuit, comprising the followingelements, taken in the order corresponding to the direction of flow ofthe cooling liquid, from left to right in FIG. 3:

-   the water-supply box 16 a into which the cooling water enters by the    supply pipe 17 a, connected to a source of pressurized water (not    shown);-   the axial passage 24 a of the left external terminal extension 20 a    of the inductor 8 with its radial ducts 15 a that emerge at the    extremity of the annular space 11 a;-   said annular space 11 a arranged between the half tubular body 1 a    and the concentric inductor 8 so as to be capable of ensuring a    circulation of water in the vicinity of the half tubular body 1 a    and to cool it during and after its contact with the hot slab 6 as    well as to cool the left part of the inductor 8;-   the radially drilled ducts 15 c, the axial passage 26 and the    radially drilled ducts 15 d of the intermediate extension 20 c of    the inductor which connect the annular space 11 a with the space 11    b;-   said annular space 11 b arranged between the half tubular body 1 b    and the inductor 8 so as to be capable of ensuring a circulation of    water in the vicinity of the half tubular body 1 b and to cool it    during and after its contact with the hot slab 6 as well as to cool    the right part of the inductor 8;-   the radially drilled ducts 15 b and the axial passage 24 b of the    external right extension 20 b of the inductor which emerges into the    water discharge box 16 b,-   and the water discharge box 16 b equipped with an outlet pipe 17 b    to recover the cooling water in a circulating loop.

The intermediate extension 20 c of the inductor implies of course thatthe electric windings 10 be well away from this spot, but the mechanicalcontinuity between the left and right part of the inductor is ensured bythis extension that can be in steel or in the same material as the axialframe of the inductor.

In accordance with one embodiment of the invention shown in FIG. 3, saidsplit stirring roll can comprise two separate and distinctelectromagnetic inductors, one in each half tubular body: an inductor 8a in the left half tubular body 1 a and an inductor 8 b in the righthalf tubular body 1 b. According to a preferred variant of theembodiment of the invention, the inductors 8 a and 8 b are representedhere as being identical to one another and similar to the singleinductor 8 of FIG. 1 or 2.

These inductors 8 a and 8 b can be firmly connected mechanically by theintermediate extension 20 c, or detachable so as to facilitate theinstallation, but are reunited through the central support 21. As isshown in the figure, a simple interlock of the “male-female” kind inthis respect would be sufficient to ensure the mechanical connection ofthe two inductors.

However, it is clearly understood that a mechanical join of this typebetween the two inductors 8 a and 8 b is required solely to form a holdon the central support 21 when the support is a single one. In contrast,the option in which each inductor comprises its own central support onits inner end could very well be considered. In such a case, two centralsupports would be juxtaposed, one beside the other, each carried by therigid frame of the casting machine. In this case, however, a junctionwould be needed, even a flexible one but water-tight, between these twolinked inductors so as to allow the cooling water to circulate.

Another aspect that could be disadvantageous for this variant is thatthe distance between the two half tubular bodies would becorrespondingly greater and hence also the fraction of the width of thecast slab 6 left free of any mechanical support and uncooled in a deadzone at the level of the intermediate bearings. However, the resultingunwanted effects on the slab could be alleviated by providing sets ofhalf tubular bodies of variable but different lengths on the same roll.In this way, according to already well-known principles, the dead zoneswould be shifted over the width of the cast slab from one roll toanother on the height of the casting machine, with the aim ofhomogenizing by and large the perturbation after the slab has progressedsome meters in the casting direction.

However, it is understood that, whatever the chosen variant of theembodiment for the central support zone 21, one has available a stirringroll consisting of two half-rolls with two distinct inductors 8 a and 8b generating sliding magnetic fields that can be independently regulatedboth for power and for the direction of slide along the axis of theinductors, providing that one has available two electric supplies, or asingle supply capable of separately supplying each inductor. Moreover,that is why, for practical reasons, the panel with electric connectionterminals, 18 a and 18 b, respectively, is preferably selected that isthe closest to a given inductor 8 a or 8 b.

In order to better clarify the presentation, it should be recalled herethat the inductors 8 a and 8 b are of the linear polyphase type(triphasic or more usually biphasic), each requiring as many pairs ofterminal connection as there are phases of its electricity supply: twopairs for a biphase type, three pairs for a triphase type (neverthelesswith the remark that in the case of an electric installation of theinductor “without neutral output”, its number of terminals will be threefor a biphase type and three for a triphase type).

This type of inductor produces a magnetic field, whose lines of forceare on the whole oriented perpendicular to the longitudinal axis A-A ofthe inductor, and mobile, because the field can be made to slide alongthis axis in one direction or the other by simply reversing the phase ofthe electricity supply. Consequently, if two electricity supplies areavailable, or what amounts to the same thing, a duplicate supply, thenthe sliding fields can be adjusted on the two inductors 8 a and 8 b of asame stirring roll independently of one another, thereby openingparticularly interesting opportunities in regard to the possibilitiesfor setting in motion the molten metal within the slab during thecasting process.

It should be noted that such a stirring roll split into two distinctstirrers does not look any different from a stirring roll with a singleinductor. Clearly, each inductor must have the complete set of windingsin order to generate a sliding magnetic field (minimum four for biphasicinductors and six for triphasic inductors), whereas the single inductordistributes its set of windings between the left and right part; thiscan for example allow the number of pairs of poles per phase to beincreased.

On the other hand, the connections of the windings of an inductor to thephases of the electricity supply will all be guided, preferably, towardthe same electrical connection panel located at one end of the roll andthe connections of the other inductor will all be guided toward theother connection panel installed at the other end of the roll (here theconnections 18 a toward the nearest panel 19 a and the connections 18 btoward the panel 19 b), whereas with a single inductor, half of theconnections can be grouped together on the left and the other half onthe right.

It is evident that neither in the case of a split stirring roll with asingle inductor (FIG. 2), nor in the case of two distinct inductors(FIG. 3), is it required to provide connections through the intermediatecentral extension 20 c of the inductor which would otherwise complicatethe design and the assembly of the installation.

The stirring rolls according to the invention, in their embodimentwithout a central support 21, can be integrated without any particulardifficulty to a segment of the structure of the casting machine equippedwith other customary support rolls and guide rolls for the slab. This isalso true for the split stirring rolls according to the invention,because the customary support rolls are likewise equipped withintermediate bearings or with intermediate supports in the case of widemachines and the structure of the segments is already designed withcentral supports.

From this observation it can be deduced that the un-split stirring rollswith a single tubular body, therefore without a central support, inaccordance with the invention, should rather be reserved for the castingof slabs with a classical width, i.e. up to about 1650 mm. Over andabove, one would prefer split stirring rolls with two half tubularbodies and a central support, although it should be emphasized thatthere is no reason not to use them even for casting slabs with acustomary width.

As a non-limiting example for casting wide slabs of the order forexample of 2000 mm, use can be made of split stirring rolls with twodistinct inductors, each with a tubular body of about 1000 mm in length,with a central support of about 10 mm width. The diameter of the halftubular bodies can be about 240 mm or more.

In a variant, for at least some of the split stirring rolls with acentral support which equip a machine for the continuous casting ofslabs, the lengths of the two half tubular bodies can be unequal. Infact, that the cast slab is not guided on the width of the centralsupport, means that the part of the slab passing next to this “hole” canswell up. Also, planning for split stirring rolls having contiguous halftubular bodies of unequal length, by therefore shifting their centralsupport such that it is placed between two successive split stirringrolls, will ensure that it will not always be the same part of the widthof the slab that will swell up. Accordingly, this will avoid as neededany flaws in the slab, such as cracks and porosities, caused by theswelling.

It can be seen that the bearings of the tubular body may be exposed tothe heat of the slab to a much greater extent during casting than in thetechnology of the prior art of stirring rolls with supporting spindlesthat are offset on both sides of the tubular body. In a variant, it canconsequently be advantageous to select helicoidal thermal deformationbearings for the tubular bodies. This type of mechanical bearing iscommercially available. In this regard, solely for informationalpurposes, mention may be made of the bearings manufactured andcommercialized by the German company “Maschinenfabrik Joseph EICH KGGmbh”.

Obviously, the invention should not be limited to the describedexamples, but should extend to a plurality of variants or equivalents,in so far as they are as defined by the claims presented below.

For example, it is understood that the term “spindle” used to designatethe supporting elements mounted at the ends of the or the two tubularbodies that are constituents of a split stirring roll, encompasses alltransmission organs that are capable of ensuring a water-tight, rigidconnection between the tubular bodies and the roller bearings that carrythem in free axial rotation.

What we claim is:
 1. A stirring roll for a continuous casting machine ofmetallic products having a broad cross section, such as a slab,comprising: (a) at least one external axially rotating tubular body madeof non-magnetic steel intended to come into contact with the surface ofa wide face of the cast slab, (b) mechanical connection elements thatensure the support of the tubular body while allowing it to freelyrotate axially, (c) support elements of the stirring roll located onboth sides beyond the limits of the tubular body and fixed to the rigidframe of the casting machine, (d) internal electromagnetic equipmentconsisting of at least one polyphasic linear inductor with a slidingmagnetic field, mounted coaxially with the tubular body so as to providean annular space between them for the circulation of a cooling liquid,said equipment forming an axial shaft equipped with end extensions thatcome to rest blocked against axial rotation on said support elements,said end extensions being hollow to allow the passage of cooling liquidand the passage of the electrical connections of the inductor, and (e)inlet/outlet boxes for cooling liquid equipped with electricalconnection terminals and mounted on the ends of the terminal extensionsof the inductor beyond said support elements; stirring rollcharacterized in that the tubular body (1) bears on the inductor (8) bymeans of said mechanical connecting elements formed by the bearings (3)located between said tubular body and the terminal extensions (20) ofthe inductor.
 2. The stirring roll according to claim 1, characterizedin that it comprises two separate aligned half tubular bodies (1 a, 1 b)equipped with mechanical connection elements with an intermediateextension (20 c) of the inductor without electric windings, and acentral support (21) connected to the rigid frame (5) of the castingmachine, said mechanical connection elements being formed by at leastone intermediate bearing (3 c, 3 d) carried by said intermediateextension (20 c) and the latter being supported by said central support(21).
 3. The stirring roll according to claim 2, characterized in thateach half tubular body (1 a, 1 b) incorporates its own inductor (8 a, 8b).
 4. The stirring roll according to claim 2, characterized in thatsaid intermediate bearing is a single bearing, common to the two halftubular bodies (1 a, 1 b) and fixed on both of its sides to the latters'ends.